Well I tried it in the early hours of this morning.. when I couldn't sleep and was looking for something to pass the time.
Amazingly I got down there.. and even more amazingly i got back up.. but altho' I could raise my torso off the floor.. lying in the same position as ''Ron'' is in the picture that Ronni posted.. I just couldn't get my legs ..or more precisely my knees to lift off the floor...

i just looked up some info on the exercise. The almost whole body benefits intrigued me.
While it doesn't say anything about intervals between short holdings as you build up to the minimum of 5 minutes daily for the full benefits from it, it does say that when you are beginning you can rest knees on floor till your arms and thighs get more capable of supporting you for longer. They also say to start with 1 1/2 minutes and build up to 5 minutes in 30 second increments, but it is clear by the photos their target audience is 30 somethings. i have no doubt, however that someone who had been doing regularly (daily or even 4 times a week) could continue to do, it properly well into their 70s-80s barring any serious injuries or health issues.
I also think older folks could come to do it the 5 minutes a day by adapting the 'schedule' for building up to that to their individual tolerance, abilities, needs. i'm going to give it ago and will let y'all know how it goes even if i abandon it. The hardest part for me will be investing the time to 'work' up to the recommended time, tho that should be easier as doing it routinely strengthens my muscles.
i could only manage 30 seconds full plank (knees up) easily, but had no trouble getting down and up, and if i thought i was going to, i would simply make sure to do it where something to use to get up was near enough. Learned along time ago you stop anything (swimming, physical games, splitting wood, heavy house cleaning, weeding) BEFORE you feel totally exhausted. Especially now that i tire more quickly than when younger and it takes me much longer to 'recuperate' from the exhaustion.
Oh, and here's link to that article in case anyone wants to read it in full, it also includes instructions for what they call 'side plank', where only 1 arm and side of foot are supporting you.
https://sport.onehowto.com/article/how-to-do-plank-exercises-correctly-4887.html